Synthesis, structure and optical properties of two uranyl oxalate complexes templated by protonated amines

Abstract

[C6H14N]4[UO2(C2O4)2(HC2O4)]NO3•2H2O (CHA) and [C8H18N][UO2(C2O4)(NO3)] (NNDMCHA) were synthesized by volatile method at room temperature, using [C6H14N] + and [C8H18N] + as templates, respectively. The structures and optical properties were characterized by combination of single-crystal X-ray diffraction, PXRD, TG-DSC, IR, Raman, UV-Vis and fluorescence spectra. CHA and NNDMCHA crystallized in monoclinic system, and space group P21/c. The equatorial coordination number of CHA and NNDMCHA are 5 and 6, respectively, forming pentagonal bipyramid and hexagonal pyramid. The lattice water in CHA formed O-H•••O hydrogen bonds with the oxygen atoms of the mononuclear anions, resulting in a s-shaped anion chain which extended along the c direction. The protonated amines were linked to the anion chains by N-H•••O and C-H•••O hydrogen bonds, leading to form the larger hexagon and the smaller parallelogram pores, respectively. The photoflurescence of two complexes significantly decreased when exposure under UV light, showing potential application for fluorescent sensor.